A Wells turbine has inherent disadvantages: Lower efficiency and poorer starting characteristics. Providing guide vanes on either side of the rotor could be one of the most effective ways of improving its performance. Several papers have demonstrated the usefulness of 2D guide vanes so far. In order to achieve further improvement in the performance of the Wells turbine, the effect of 3D guide vanes has been investigated experimentally by testing a model under steady flow conditions. Then, the running and starting characteristics under irregular flow conditions have been obtained by a computer simulation using quasi-steady analysis. It is found that the running and starting characteristics of the Wells turbine with 3D guide vanes are superior to those with 2D guide vanes. © 2000 Elsevier Science Ltd. All rights reserved.